The Yellow Blanket of Spring

Image of pine tree pollen in flight. Photo courtesy of <a href="">Amy Campion</a>

Image of pine tree pollen in flight. Photo courtesy of Amy Campion.

For a few weeks every spring, Chapel Hill and Carrboro are covered in a yellow blanket of pine tree pollen and everything’s a mess. Birches, oaks, pines, and more get the signal to “spread the love” and distribute their genetic material all over the place, irritating our eyes and noses. But how do plants know when it’s time to release their pollen? You may have learned in elementary school that warm weather activates the flowering gene in plants. While temperature plays a role, it is not the only trigger. Remember that random week of warm weather we had at the end of February? Why didn’t the pine trees start distributing their pollen then?
Spring ushers in longer days along with warmer weather. The amount of daylight a hemisphere receives changes as the Earth orbits the sun. In the winter, our hemisphere (the northern one) tilts away from the sun, reducing the amount of sunlit hours in the day. In the summer, our hemisphere tilts toward the sun. This means that between the winter and summer solstices, as the Northern Hemisphere transitions from tilting away from the sun to tilting towards it, the amount of daylight increases.
The changing length of day throughout the year being a consistent phenomenon, plants have developed a mechanism that uses the amount of daylight as an indicator to flower. The photoreceptors that allow sunlight to enter and initiate photosynthesis, the process by which plants transform light into energy, also activate proteins. Thus more daylight means more protein. And once enough protein builds up, the plant gets the signal to flower.
Imagine the protein as sand in an hour glass. When the sun rises, you flip the hourglass and sand begins to trickle down. After the sun sets, you flip the hourglass back over and the sand that built up during the day pours out. During the winter, all the sand that builds up during the day will empty at night because the nights last longer than the days. As you approach spring, each day the sun is up a little longer, meaning a little more sand can accumulate. At a certain point, your hourglass will build up enough sand during the day that some will still remain at the end of night. Once the protein reaches this threshold, the flowering gene in plants can activate.
But what if the days have lengthened and it is still cold out? If it’s too cold there won’t be bugs or other animals around to help spread the pollen. Thus, plants also rely on the temperature as a secondary indicator. This is where things have recently started to get messy. Global climate change has reduced the number of lingering cold days in the transition from winter to spring. As a result, scientists have noticed that plants are flowering earlier, and allergy season is starting earlier and lasting longer than in previous decades. So, if you’ve noticed your nose itching sooner and you can’t seem to shake your sniffles, you’re not crazy.

Fortunately, there are steps you can take to reduce your allergy symptoms while you wait for those cleansing April showers. Rain will reduce the amount of airborne pollen and wash away the pollen that blankets your car, creating little yellow rivers that will whisk away the pine trees’ genetic material. Then Chapel Hill will once again be Carolina Blue—until next year.

Peer edited by Rachel Haake & David Seamans

Global climate change: How does it happen, and is there hope?

The coming of the New Year often brings about feelings of nostalgia as we reminisce about the previous calendar year. Looking back at 2015, we as humans have quite a bit to be proud of: the granting of women’s voting rights in Saudi Arabia, the development of a new highly effective drug for the prevention of HIV infection, and of course, the new Star Wars film. However, arguably one of the most significant accomplishments of 2015 was the Paris Agreement – the first-ever universal, legally-binding global climate deal.

Continue reading

Traveling trees: how fast can they migrate to track climate change?

Most readers are probably familiar with some of the implications of climate change: sea level rise; more frequent extreme weather events; habitat loss for arctic species. Other implications are equally important to understand and reach into many realms of ecology (as well as other disciplines), but are not popular topics covered in the media. Continue reading

The Balance of Earth’s Carbon Cycles

Life requires balance. We spend a large part of our existence balancing our careers and our personal lives, our family and work obligations, and our own personal health. If something occurs that displaces one of the elements of our lives, we take action to bring it back into balance. The Earth is no different. Our planet uses carbon to regulate its temperature with three processes; the geological carbon cycle, the ice-albedo effect, and the biological carbon cycle.
Before Earth had life, two main processes worked together as a thermostat to keep the planet in equilibrium; the geological carbon cycle and the ice-albedo effect. The geological carbon cycle acts over millions of years, slowly pulling carbon dioxide (CO2) from the atmosphere into the Earth’s mantle and then releasing it back into the atmosphere. The process begins when CO2 in the atmosphere combines with water to create carbonic acid, a weak acid that rains down onto the land. Carbonic acid gradually eats away at rocks, breaking them down into various atoms that are missing electrons, known as ions. Rivers carry these ions into the ocean where they readily combine with carbon already present, creating limestone, which sinks to the bottom of the ocean. As plate tectonics slowly renews the Earth’s surface, the ocean floor is forced down into the Earth’s mantle and the calcium carbonate is melted down. Active volcanoes later release this material and the CO2 in it back into the atmosphere.
Where did the carbon in the shallow depths of the ocean originate? The ocean absorbs CO2 from the atmosphere using simple chemistry. When CO2 is dissolved in water, a hydrogen molecule is released. This hydrogen can react with some of the ions from chemical weathering to create bicarbonate molecules. The bicarbonate combines with calcium released during weathering to create calcium carbonate (i.e. limestone), which settles onto the ocean floor.
Artists impression of a snowball Earth. Source: <a href=""></a>

Artists impression of a snowball Earth. Source:

A full turn of the geological carbon cycle happens on the order of a few million years. This process works in conjunction with the second ancient process, the ice-albedo cycle. Together, these two processes cause Earth’s temperature to oscillate between warm and cold periods. The ice-albedo cycle works much faster than the geological carbon cycle, on the order of tens of thousands of years. Like the geological carbon cycle, it is intimately tied to the Earth’s temperature. An object’s albedo defines how much sunlight it reflects, with a higher albedo meaning more reflection. Ice and clouds raise the albedo of a planet. If temperature decreases on Earth, causing the ice caps to grow, more of the Sun’s light is reflected back into space before entering the atmosphere. This means that the Earth’s ocean and land do not absorb as much solar radiation and cannot warm. This causes the Earth to cool further and increase the area the ice caps cover. Without the geological cycle to regulate this process, the Earth would be covered in ice.

As the polar ice caps grow, more and more of the water necessary for chemical weathering is frozen. This halts the chemical weathering process, causing CO2 to build up in the atmosphere and trap the sunlight that is not reflected back into space. As a result, Earth begins to warm, melting the ice caps and liberating more water to be used for chemical weathering.
Currently, volcanoes release up to 380 million metric tons of CO2 into the atmosphere per year. The amount of CO2 that is drawn out of the atmosphere due to chemical weathering depends on the rains but is not significant compared to the amount released and absorbed during the biological carbon cycle.
Occurring on time spans that match our own, the biological carbon cycle is fueled by plants. CO2 from the atmosphere is combined with water during photosynthesis to create sugars and oxygen. These sugars are then broken down for energy by living organisms and fires. After the sugars are broken down and used, the remaining molecules recombine with oxygen to recreate water and CO2. The CO2 then returns to the atmosphere, and the cycle starts anew. During this entire process, 120 Gigatons of CO2 is absorbed from and reemitted into the atmosphere. This is approximately 1000 times more than the amounts discussed during the geological carbon cycle, and it affects the global temperature on much shorter and more noticeable timescales.
Cartoon of Earth's Carbon Cycles. Courtesy of <em>Climate Placemat: Energy-Climate Nexus</em>, US Department of Energy Office of Science. (p.1)(<a href="" target="_blank">website</a>)

Cartoon of Earth’s Carbon Cycles. Courtesy of Climate Placemat: Energy-Climate Nexus, US Department of Energy Office of Science. (p.1)(website)

These are the carbon cycles that were in place on Earth before the industrial revolution. Humans have added an additional cycle to the planet. We contribute to the carbon levels in the atmosphere through emissions, when we burn harvested carbon deposits like coal and oil. Currently, human activity is emitting 9 Gigatons of CO2 per year into the atmosphere through fossil fuel burning. Our carbon footprint is between the geological and biological carbon cycles and the Earth is struggling to use up the additional CO2 that we’ve put there. This extra CO2 is being absorbed by the oceans, causing them to become more acidic. It is causing plant life to decrease the number of stomata they grow, so they do not intake more CO2 than is necessary. The added CO2 is causing the Earth to warm faster than any of the more ancient carbon cycles can cool it off. Humans are now a significant CO2 contributor to our planet. Just as we maintain balance in our own lives, we must take steps to ensure that our contributions do not throw a wrench in the carbon cycles already in place on our planet.

Peer edited by Suzan Ok & Holly Bullis

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This article was co-published on the TIBBS Bioscience Blog.

Underfoot, but not to be underrated: how tiny soil creatures influence survival, growth, and communication of plants

Traditionally, plant ecologists seeking to better understand plant communities looked up (at light availability or precipitation patterns), across the landscape (at elevation or topography), and down (at leaf litter depth or soil moisture). More recently, however, they’re starting to look below. Continue reading

Arctic Tales of Icy Trails

Far out in eastern Russia, deep in the Siberian Plateau, lies one of the great waterways of the world. 

The Lena is the eleventh longest river on Earth. For thousands of treacherous kilometers, she makes her way through forests and across tundra, eventually delivering her waters into the icy cradle of the Arctic Ocean. The power of these frigid landscapes is such that for six months out of the year, the surface of the Lena is completely frozen.

The freeze starts with the deepening chill of October and extends through black December twilights and a solemn New Year.

Even when fresh springtime breezes arrive, melting the ice, the Lena pays a terrible price for her freedom. The sheets of ice do not yield peacefully, drop by drop, in a quiet surrender to the warmth. Instead, the process is rife with violence. As some parts of the ice destabilize, the flow of the river increases suddenly, and before the ice has a chance to melt, it sweeps downstream, displacing and spilling water over the banks and causing major flooding. This process is called “ice break-up.”

Very few people live along the vast plain where the Lena alternates between flow and ice. Near the Arctic Circle, a lonely station is the last shivering wisp of human life before the river dissolves into its northern grave.

Sarah Cooley in the lovely Scandinavian dream of Iceland, just one of the countries where she has pursued her polar studies as a UNC student.

Sarah Cooley in the lovely Scandinavian dream of Iceland, just one of the countries where she has pursued her polar studies as a UNC student.

Records made at this station over several decades indicate the precise date in spring when the Lena breaks free of her icy grip – the precise date when the ice crumbles and the entire river flows again. Over the past years, this date on which the ice breaks has crept earlier and earlier.

Thousands of miles away, in an office at UNC, sits Sarah Cooley. She has never been to Russia, nor seen the Lena with her own eyes, so she cannot tell you about its beauty, or ferocity, or chill. However, she has seen the Lena plenty through images. These are not images captured by a camera, but rather images captured by satellites, whose falcon-like eyes see much from their distant orbits. Can careful mastery and manipulation of these images tell us something about ice break-up on the Lena, something beyond the comprehension of a single station outpost?

It was August 2014, and Sarah was preparing to start her senior thesis. She wanted to focus on glaciers and satellites, so she went to find Dr. Tamlin Pavelsky, a professor in the geology department, whose earlier research focused on ice break-up in Arctic Rivers. However, Dr. Pavelsky completed his project in 2004, during the infancy of the newly-launched Terra and Aqua satellites. These satellites carry onboard quite a remarkable instrument called MODIS.

Although its name makes every aspiration at modesty, MODIS has much of which to be proud. Since 2000, the MODIS sensor has snapped images of the entire planet, every day. That means hundreds of thousands, if not millions, of images dedicated just to Arctic rivers like the Lena are available, free of charge, on a NASA website.

Now that MODIS is fifteen years old, her idea was to recreate Dr. Pavelsky’s project, incorporating the many extra years of data into the study. The first step required Sarah’s full familiarity with the NASA LAADS website, from which she had to download over 16,000 satellite images.

“It might be the most images anyone’s ever ordered before,” Sarah explains. The four Arctic Rivers she studied stretch out over 18 MODIS scenes. For each of those 18 scenes, Sarah downloaded 60 days’ worth of images over the fifteen years of MODIS’ existence. The sixty days were centered on March, April, and May, since that is the window in which the ice break-up occurs. Eighteen scenes on sixty days for fifteen years added up quickly!

It took Sarah three months to acquire her full library of images. The ordering process is not too difficult, “but then you have to wait for it, and when you get it, it’s not always what you expected, it might have errors, or wrong dates and be the wrong place.”

These images from MODIS show the progression of ice break-up on the Lena River of Russia. Where the river shows white, it is frozen ice. The white slowly overtaken by black water indicates that the ice is disappearing.

Nevertheless, after a Christmas break spent watching Sherlock and trying the utter patience of the NASA LAADS website, Sarah eventually was ready to proceed with her analysis of those thousands of images.

The thing to know about satellite images is that they are not precisely like the pictures we might snap, with ambitions of posting to Facebook and getting 100 likes.

A satellite image is a record of how much light is being reflected off the surface of the Earth – and not just the ordinary, commonplace lights like blue light, red light, and green light. Satellites also venture into the realms of light humans can’t see, such as near-infrared light, and short-wave infrared light, and all sorts. The falcon eyes of MODIS captures these wavelengths of light, then translates its findings into simple numbers that computers and brains can interpret and analyze.

Sarah was sitting on a trove of 16,000 MODIS images of near-infrared light. But can near-infrared light actually tell us anything about ice in Arctic rivers? This is where Sarah had to experiment.

She found that when the Lena was frozen, it reflected almost all near-infrared light that reached it. On the other hand, when the river was an unshackled tumult of free-flowing water, its reflectance was very low. And when the river was a mix of ice and water, its reflectance value was somewhere in between.

Sitting in her warm office thousands of miles away, Sarah started watching the progression of ice break-up on the Lena by using near-infrared light as the key to unlock her satellite images.

With her reflectance data in hand, Sarah sliced her northern rivers into ten kilometer slabs. Then, like a child playing with its food, each slab was cut into impossibly tiny 250 meter pixels. For all her MODIS images, Sarah counted up which of her tiny pixels crossed the threshold that equaled ice; which lay in the range of water; and which belonged to the brew that denotes a mixture of ice and water.

On the day that 75% of the tiny pixels in a given slab passed the threshold that implies water, that slab was declared to have undergone its spring melting. This method finds the exact date that each slab of river melted, allowing detailed analysis of melting time on a year to year basis. It means that instead of a single date of ice break-up provided by a lonely station near the Arctic Circle, Sarah can now produce an estimate of when ice break-up is happening along the entire river.

It’s a very straightforward approach, and that’s one of the things Sarah likes about MODIS. “I really enjoy the simplicity, and it being daily is great. You can really do a lot with it.”

Of course, Sarah did not count all of the pixels and separate them into categories by hand. Instead, she wrote a series of computer scripts that did the work. The first part of her script classified the MODIS images into land, water, ice, and ice and water mixture. Then, all clouds were removed. Finally, computers calculated the amount of ice melt in each 10-kilometer slab. These scripts took three hours to run per river, much preferable to the hundreds of tedious hours it would take to do by hand. Now the scripts can be passed on and used by others, absorbing the newer images that MODIS keeps adding to its archives.

It is quite an achievement, especially compared to how Sarah felt when she first arrived at UNC as a freshman and saw older classmates doing sophisticated projects.

She remembers vividly thinking: “Oh my gosh, I can never do that. Now I realize I can do so many more things than I ever thought I could. And I realize that learning all those things isn’t something that happens overnight, it’s something you learn by taking classes, doing research, working in the lab. And now I’m never intimidated by coding. I love coding and seeing the things I can do with it.”

We are now in the waning days of April, and Sarah will soon graduate from UNC Chapel Hill. She and Dr. Pavelsky are finalizing a paper on their results.

After UNC, Sarah is moving to England to complete a Masters of Philosophy degree in Polar Studies at Cambridge University as a Gates Cambridge Scholar. Showing a persistent interest in Arctic ice, she plans to focus on glacier flow in Greenland.

Sarah fell in love with Greenland and wanted to pursue polar science ever since she studied abroad in Denmark and visited the Greenland ice sheet. “It’s really cool being out there, and there’s people, wildlife. Some people like to study polar science in Antarctica, but to me, it seems so empty. I like how in the Arctic everything feels connected to the people and the land.”

Meanwhile, the Lena still succumbs to the bleak icy thrall that envelops her every October, from which she cannot relax until the spring ice break-up, which every year creeps earlier in the calendar. Signs of climate change are everywhere.

Will the river change its melting patterns? Will its ice break-up involve more flooding in the future, or will it occur in irregular patches that do not progress linearly down its Siberian route? All of these are questions that satellites, ground station data, and scientists like Sarah can help to answer.

Peer edited by Chris Givens and Chelsea Boyd. 

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